Sources and reactivity of NMHCs and VOCs in the atmosphere: a review.

Nonmethane hydrocarbons (NMHCs) and volatile organic compounds (VOCs) are important species present in the environment, which results in alteration of the chemistry of atmosphere. On the global scale natural emissions of NMHCs and VOCs exceed anthropogenic emissions, although anthropogenic sources usually dominate within urban areas. Among the natural sources, vegetation is the dominant source. Oceanic and microbial production of these species is minimal as compared to other sources of input. Isoprene and terpenes are main species of NMHCs which are emitted from plants as a protective mechanism against temperature stress tolerance and protection from ravages of insects and pests. The major anthropogenic sources for NMHCs emissions are biomass burning and transportation. NMHCs play a significant role in ozone (O(3)) production in the presence of adequate concentration of oxides of nitrogen in the atmosphere. The production of O(3) is based on Maximum Incremental Reactivity (MIR) of NMHCS and VOCs. The compound's MIR multiplied by molecular weight gives Relative Ozone Productivity (ROPi). To check the reliability of current methods of measuring the NMHCs the Nonmethane Hydrocarbon Inter-comparison Experiment (NMHICE) had been designed. The sample of known composition and unknown concentration of different hydrocarbons was supplied to different laboratories worldwide and less than 50% laboratories correctly separated the unknown mixture. Atmospheric scientists throughout the world are evaluating current analytical methods being employed and are trying to correct the problems to ensure quality control in hydrocarbon analysis.